An effective method to understand photo-generated charge transfer processes of Z-scheme Ti/α-Fe2O3/g-C3N4 photocatalysts for hydrogen evolution

Unraveling the Synergistic Mechanism of Boosted Photocatalytic H2O2 Production over Cyano-g-C3N4/In2S3/Ppy Heterostructure and Enhanced Photocatalysis-Self-Fenton Degradation Performance

In this work, cyano contained g-C3N4 comodified by In2S3 and polypyrrole (C≡N─CN/IS/Ppy) materials are synthesized for the photocatalytic production of H2O2 and photocatalysis-self-Fenton reaction for highly efficient degradation of metronidazole. The results from UV-vis spectrophotometry, surface photovoltage, and Kelvin probe measurements reveal the promoted transport and separation efficiency of photoinduced charges after the introduction of In2S3 and Ppy in the heterojunction. The existence of a built-in electric field accelerates the photoinduced charge separation and preserves the stronger oxidation ability of holes at the valence band of C≡N─CN. Linear sweep voltammetry measurements, zeta potential analyzations, nitroblue tetrazolium determination, and other measurements show that Ppy improves the conversion ratio of •O2 - to H2O2 and the utilization ratio of •O2 -, as well as suppresses decomposition of H2O2. Accordingly, the H2O2 evolution rate produced via a two-step single-electron reduction reaction reaches almost 895 µmol L-1 h-1, a value 80% and 7.2-fold higher than those obtained with C≡N─CN/IS and C≡N─CN, respectively. The metronidazole removal rate obtained via photocatalysis-self-Fenton reaction attains 83.7% within 120 minutes, a value much higher than that recorded by the traditional Fenton method. Overall, the proposed synthesis materials and route look promising for the H2O2 production and organic pollutants degradation.

Defect Engineering and Surface Polarization of TiO2 Nanorod Arrays toward Efficient Photoelectrochemical Oxygen Evolution

The relatively low photo-conversion efficiencies of semiconductors greatly restrict their real-world practices toward photoelectrochemical water splitting. In this work, we demonstrate the fabrication of TiO2-x nanorod arrays enriched with oxygen defects and surface-polarized hydroxyl groups by a facile surface reduction method. The oxygen defects located in the bulk/surface of TiO2-x enable fast charge transport and act as catalytically active sites to accelerate the water oxidation kinetics. Meanwhile, the hydroxyl groups could establish a surface electric field by polarization, for efficient charge separation. The as-optimized TiO2-x nanorod photoanode achieves a high photocurrent density of 2.62 mA cm−2 without any cocatalyst loading at 1.23 VRHE under 100 mW cm−2, which is almost double that of the bare TiO2 counterpart. Notably, the surface charge separation and injection efficiency of the TiO2-x photoanode reach as high as 80% and 97% at 1.23 VRHE, respectively, and the maximum incident photon-to-current efficiency reaches 90% at 400 nm. This work provides a new surface treatment strategy for the development of high-performance photoanodes in photoelectrochemical water splitting.

Protrudent electron transfer channels on kaolinite modified iron oxide QDs/N vacancy graphitic carbon nitride driving superior catalytic oxidation

Optimizing electron transfer channels and sufficiently exposing active sites to trigger an efficient Fenton-like reaction are vital for manipulating catalytic properties of water treatment. Herein, Fe₂O₃ quantum dots were prepared and integrated with composites of g-C₃N₄ and kaolinite with nitrogen (N) vacancies (FONGK-10) for bisphenol A (BPA) removal in a peroxymonosulfate (PMS)/visible light (Vis) system. X-ray absorption near-edge structures and extended X-ray absorption fine structures demonstrated interface's combined properties. In particular, the tight interfacial contact and introduction of N vacancies resulted in the formation of effective electron channels, which caused more effective separation of electron-hole pairs and an extended response time of 1.5 × 10^-4 s. Furthermore, the introduction of kaolinite reduced the Fe₂O₃ particle size and accelerated PMS consumption. The k value in FONGK-10/PMS/Vis system was 4.5 times that of the FONGK-10/PMS and 27.5 times that of the FONGK-10/Vis system, and the synergetic system exhibited superior consecutive catalytic performance in a fluidized-bed catalytic unit, degrading ~100% of BPA in 200 min. The exposed electron channels significantly maintained the Fe(III)/Fe(II) stable dynamic cycle, thereby enhancing the activation of PMS and photocatalysis performance.

MoS2 and Fe2O3 co-modify g-C3N4 to improve the performance of photocatalytic hydrogen production

Photocatalytic hydrogen production as a technology to solve energy and environmental problems exhibits great prospect and the exploration of new photocatalytic materials is crucial. In this research, the ternary composite catalyst of MoS2/Fe2O3/g-C3N4 was successfully prepared by a hydrothermal method, and then a series of characterizations were conducted. The characterization results demonstrated that the composite catalyst had better photocatalytic performance and experiment results had confirmed that the MoS2/Fe2O3/g-C3N4 composite catalyst had a higher hydrogen production rate than the single-component catalyst g-C3N4, which was 7.82 mmol g−1 h−1, about 5 times higher than the catalyst g-C3N4 (1.56 mmol g−1 h−1). The improvement of its photocatalytic activity can be mainly attributed to its enhanced absorption of visible light and the increase of the specific surface area, which provided more reactive sites for the composite catalyst. The successful preparation of composite catalyst provided more channels for carrier migration and reduced the recombination of photogenerated electrons and holes. Meanwhile, the composite catalyst also showed higher stability and repeatability.

Revealing long-lived electron–hole migration in core–shell α/γ-Fe2O3/FCP for efficient photoelectrochemical water oxidation

A γ/α-Fe2O3/FCP photoanode with rapid interfacial hole injection and long-lived charge separation states (∼50.64 ps) showed that the synergistic effect of a phase junction and FeCo Prussian blue (FCP) could optimize the kinetics in water oxidation.

Simple electrodeposition to synthesize a NiFeSx-modified Ti-Fe2O3 photoanode: an effective strategy to improve the photoelectrochemical water oxidation reaction

Decorating a high-efficiency oxygen evolution reaction (OER) electrocatalyst as a cocatalyst on an α-Fe₂O₃ photoanode is known to be one of the most efficient methods to improve the photoelectrochemical (PEC) water oxidation activity. In our work, different from traditional methods of transition metal sulfide cocatalyst synthesis, an NiFeS_x-decorated Ti-Fe₂O₃ photoanode is synthesized through a simple one-step electrodeposition method, which benefits the interface between Ti-Fe₂O₃ and NiFeS_x. With the help of this excellent OER electrocatalyst, the photocurrent density of the NiFeS_x-Ti-Fe₂O₃ photoanode rises to 3 mA cm^-2 at 1.23 V vs. RHE, which is 2.5 times greater than the photocurrent of Ti-Fe₂O₃. Moreover, the onset potential of NiFeS_x-Ti-Fe₂O₃ shifts negatively by 170 mV compared with that of pure Ti-Fe₂O₃. Furthermore, surface photovoltage spectroscopy (SPV) and transient photovoltage (TPV) techniques and photoelectrochemical impedance spectroscopy (PEIS) were used to analyze the true effects of NiFeS_x as an efficient cocatalyst for enhancing the PEC performance of the NiFeS_x-Ti-Fe₂O₃ photoanode. This work provides a simple method for loading a low-cost and efficient cocatalyst to modify a Ti-Fe₂O₃ photoanode for the PEC water oxidation reaction.

Design of earth-abundant Z-scheme g-C3N4/rGO/FeOOH ternary heterojunctions with excellent photocatalytic activity

A ternary Z-scheme g-C₃N₄/rGO/FeOOH heterostructure photocatalyst for H₂ production was designed and fabricated, which exhibited photocatalytic H₂ production of 124.9 and 869.8 μmol h⁻¹ g⁻¹ under visible and UV-Vis light irradiation, respectively.